This invention relates to optical systems and in particular to a strip scanning optical system for scanning an object and progressively projecting a composite image of the same at an image surface, such as a xerographic or other photosensitive surface in a photocopying process.
There are three general types of strip scanning arrangements known to the prior art. In one, the optical system is fixed and the object and photoreceptor move relative to the optics. In the second, the object is fixed and the optical system and photoreceptor move at appropriate speeds relative to the object. In the third, the object is fixed and is scanned by a rotating mirror to relay an image of the object onto a moving photoreceptor.
Typically, these prior art systems have in common the fact that they are capable of projecting a usable image only in one direction of scan motion. The return motion, whether it be return of the object, the optics, or the mirror, projects an image onto the moving photoreceptor which is disoriented (wrong reading) and therefore useless. Accordingly, the prior art has variously resorted to flyback arragements to minimize the "lost time" involved in the return motion of the scan mechanism. One system by which to accomplish scanning in both directions of object reciprocation is shown in U.S. Pat. No. 3,574,459 to Hartwig and Schnell, in which a single optical axis is rotated 180.degree. between successive scans by a prism.